226 research outputs found

    Anomalous diffusion mediated by atom deposition into a porous substrate

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    Constant flux atom deposition into a porous medium is shown to generate a dense overlayer and a diffusion profile. Scaling analysis shows that the overlayer acts as a dynamic control for atomic diffusion in the porous substrate. This is modeled by generalizing the porous diffusion equation with a time-dependent diffusion coefficient equivalent to a nonlinear rescaling of timeComment: 4 page

    Kantian Meadows: A Just Nursing Home Grounded in the Categorical Imperative

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    This dissertation examines the structures of contemporary nursing homes and argues that the structure is conducive to the objectification (treatment of a human being as a non-person) of nursing home residents. In order to eliminate the potential for objectification, this project employs the Kantian categorical imperative as its theoretical framework. Based on that framework Kantian Meadows is created as an example of a just nursing home

    Loss of strength in Ni3Al at elevated temperatures

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    Stress decrease above the stress peak temperature (750 K) is studied in h123i single crystals of Ni3(Al, 3 at.% Hf ). Two thermally activated deformation mechanisms are evidenced on the basis of stress relaxation and strain rate change experiments. From 500 to 1070 K, the continuity of the activation volume/temperature curves reveals a single mechanism of activation enthalpy 3.8 eV/atom and volume 90 b3 at 810K with an athermal stress of 330 MPa. Over the very same temperature interval, impurity or solute diffusion towards dislocation cores is evidenced through serrated yielding, peculiar shapes of stress–strain curves while changing the rate of straining and stress relaxation experiments. This complicates the identification of the deformation mechanism, which is likely connected with cube glide. From 1070 to 1270 K, the high-temperature mechanism has an activation enthalpy and volume of 4.8 eV/atom and 20 b3, respectively, at 1250 K

    Ballistic and molecular dynamics simulations of aluminum deposition in micro-trenches

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    Two different feature scale modeling frameworks are utilized for the study of aluminum (Al) deposition profiles inside micro-trenches. The first framework, which is applied in metal-organic chemical vapor deposition (MOCVD) of Al, couples a ballistic model for the local flux calculation, a surface chemistry model, and a profile evolution algorithm. The calculated conformity of the deposited film is compared with experimental results corresponding to Al MOCVD from dimethylethylamine alane (DMEAA). The outcome of the comparison is that the effective sticking coefficient of DMEAA is in the range of 0.1 - 1. There is also a strong indication that surface reaction kinetics follows Langmuir - Hinshelwood or Eley - Rideal mechanism. The second framework, which is applied in physical vapor deposition of Al, implements 2D molecular dynamics (MD) simulations. The simulations are performed in a "miniaturized" domain of some hundreds of Angstroms and are used to explore micro-trench filling during magnetron sputtering deposition of Al on a rotated substrate. Most of the experimental results are qualitatively reproduced by the MD simulations; the rotation, aspect ratio, and kinetic energy effects are correctly described despite the completely different length scales of simulation and experiment. The sticking probability of Al is calculated 0.6 for the conditions of the experiments

    Screw dislocation in zirconium: An ab initio study

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    Plasticity in zirconium is controlled by 1/3 screw dislocations gliding in the prism planes of the hexagonal close-packed structure. This prismatic and not basal glide is observed for a given set of transition metals like zirconium and is known to be related to the number of valence electrons in the d band. We use ab initio calculations based on the density functional theory to study the core structure of screw dislocations in zirconium. Dislocations are found to dissociate in the prism plane in two partial dislocations, each with a pure screw character. Ab initio calculations also show that the dissociation in the basal plane is unstable. We calculate then the Peierls barrier for a screw dislocation gliding in the prism plane and obtain a small barrier. The Peierls stress deduced from this barrier is lower than 21 MPa, which is in agreement with experimental data. The ability of an empirical potential relying on the embedded atom method (EAM) to model dislocations in zirconium is also tested against these ab initio calculations

    Flip dynamics in octagonal rhombus tiling sets

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    We investigate the properties of classical single flip dynamics in sets of two-dimensional random rhombus tilings. Single flips are local moves involving 3 tiles which sample the tiling sets {\em via} Monte Carlo Markov chains. We determine the ergodic times of these dynamical systems (at infinite temperature): they grow with the system size NTN_T like Cst.NT2lnNTCst. N_T^2 \ln N_T; these dynamics are rapidly mixing. We use an inherent symmetry of tiling sets and a powerful tool from probability theory, the coupling technique. We also point out the interesting occurrence of Gumbel distributions.Comment: 5 Revtex pages, 4 figures; definitive versio

    Pheochromocytoma diagnosed during pregnancy: lessons learned from a series of ten patients

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    BACKGROUND: Pheochromocytoma (PHEO) in pregnancy is a life-threatening condition. Its management is challenging with regards to the timing and type of surgery. METHODS: A retrospective review of the management of ten patients diagnosed with pheochromocytoma during pregnancy was performed. Data were collected on the initial diagnostic workup, symptoms, treatment, and follow-up. RESULTS: PHEO was diagnosed in ten patients who were between the 10th and the 29th weeks of pregnancy. Six patients had none to mild symptoms, while four had complications of paroxysmal hypertension. Imaging investigations consisted of MRI, CT scan and ultrasounds. All had urinary metanephrines, measured as part of their workup. Three patients had MEN 2A, one VHL syndrome, one suspected SDH mutation. All patients were treated either with α/β blockers or calcium channel blockers to stabilize their clinical conditions. Seven patients underwent a laparoscopic adrenalectomy before delivery. Three out of these seven patients had a bilateral PHEO and underwent a unilateral adrenalectomy of the larger tumor during pregnancy, followed by a planned cesarean section and a subsequent contralateral adrenalectomy within a few months after delivery. Three patients had emergency surgery for maternal or fetal complications, with C-section followed by concomitant or delayed adrenalectomy. All newborns from the group of planned surgery were healthy, while two out three newborns within the emergency surgery group died shortly after delivery secondary to cardiac and pulmonary complications. CONCLUSIONS: PHEO in pregnancy is a rare condition. Maternal and fetal prognosis improved over the last decades, but still lethal consequences may be present if misdiagnosed or mistreated. A thorough multidisciplinary team approach should be tailored on an individual basis to better manage the pathology. Unilateral adrenalectomy in a pregnant patient with bilateral PHEO may be an option to avoid the risk of adrenal insufficiency after bilateral adrenalectomy

    Impact of body mass index on post-thyroidectomy morbidity

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    BACKGROUND: The impact of obesity on total thyroidectomy (TT) morbidity (recurrent laryngeal nerve palsy and hypocalcaemia) remains largely unknown. METHODS: In a prospective study (NCT01551914), patients were divided into five groups according to their body mass index (BMI): underweight, normal weight, overweight, obese, and severely obese. Preoperative and postoperative serum calcium was measured. Recurrent laryngeal nerve (RLN) function was evaluated before discharge, and if abnormal, at 6 months. RESULTS: In total 1310 patients were included. Baseline characteristics were similar across BMI groups except for age and sex. Postoperative hypocalcaemia was more frequent in underweight compared to obese patients but the difference was not statistically significant in multivariate analysis. There was no difference between groups in terms of definitive hypocalcaemia, transient and definitive RLN palsy, and postoperative pain. CONCLUSION: Obesity does not increase intraoperative and postoperative morbidity of TT, despite a longer duration of the procedure

    Advanced age does not increase morbidity after total thyroidectomy. Result of a prospective study

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    BACKGROUND: It is well known that total thyroidectomy is feasible on elderly patients but is linked to complications because of their underlying comorbidities. In this study we analyzed the specific risks linked to surgery, hypoparathyroidism and recurrent nerve palsy. METHODS: materials-methods:Prospective, multicentre trial conducted at 13 hospital sites. The primary endpoint was the percentage of patients with postoperative hypocalcaemia (albumin-corrected serum calcium level <2 mmol/L at day 2). Secondary endpoints included recurrent nerve palsy rate at day 2, the percentage of patients with hypocalcaemia (serum calcium level <2 mmol/L) and recurrent nerve palsy at month 6, operating durations and postoperative pain. Patients were separated in two groups: <70 years and ≥70 years old. RESULTS: In total, 1329 patients who underwent total thyroidectomy were included (median age 51.17 years [18.10; 80.90], 80% women, and hyperthyroidism in 20%, 101 ≥ 70 years old). Rates of hypocalcaemia at day 2 and month 6 were 20.02% and 1.98% respectively. Nasofibroscopy showed postoperative abnormal vocal cord motility in 9.92% cases (hypo-motility 5.76% - immobility 4.16%) and 0.95% at month 6 (hypo-motility 0.48%, immobility 0.48%). Patients ≥70 years had a lower (but non-significant) postoperative and definitive hypocalcaemia rate than patients < 70 years: 14.85% vs 20.44% at day 2 (p = 0.1773) and 0% vs 2.15% at month 6 respectively (p = 0.2557). Abnormal vocal cord motility rate was 12.00% in patients ≥70 years vs 9.75% in patients <70 years at day 2 (p = 0.4702), and 2.06% in patients ≥70 years vs 0.86% at month 6 (p = 0.2340). CONCLUSIONS: Total thyroidectomy in patients ≥70 years is feasible and safe. Age does not increase the morbidity. The study is registered with ClinicalTrials.gov number NCT01551914
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